.Net: Hook up memory in SequentialPlanner examples (microsoft#2196)

### Description
Adding the memory configuration and some comments to the
SequentialPlanner samples in KernelSyntaxExamples.

### Contribution Checklist
- [X] The code builds clean without any errors or warnings
- [X] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [X] All unit tests pass, and I have added new tests where possible
- [X] I didn't break anyone 😄

dotnet/samples/KernelSyntaxExamples/Example12_SequentialPlanner.cs

@@ -177,6 +177,8 @@ private static async Task MemorySampleAsync()
     {
         Console.WriteLine("======== Sequential Planner - Create and Execute Plan using Memory ========");
 
+        // IMPORTANT: Register an embedding generation service and a memory store. The Planner will
+        // use these to generate and store embeddings for the function descriptions.
         var kernel = new KernelBuilder()
             .WithLogger(ConsoleLogger.Logger)
             .WithAzureChatCompletionService(
@@ -210,7 +212,8 @@ private static async Task MemorySampleAsync()
 
         var goal = "Create a book with 3 chapters about a group of kids in a club called 'The Thinking Caps.'";
 
-        var planner = new SequentialPlanner(kernel, new SequentialPlannerConfig { RelevancyThreshold = 0.5 });
+        // IMPORTANT: To use memory and embeddings to find relevant skills in the planner, set the 'Memory' property on the planner config.
+        var planner = new SequentialPlanner(kernel, new SequentialPlannerConfig { RelevancyThreshold = 0.5, Memory = kernel.Memory });
 
         var plan = await planner.CreatePlanAsync(goal);